Re: [RFC PATCH 5/5] ref-filter: add docs for new options

Olga Telezhnaya [off-list ref] writes:

 objectname::
 	The object name (aka SHA-1).
 	For a non-ambiguous abbreviation of the object name append `:short`.
 	For an abbreviation of the object name with desired length append
 	`:short=<length>`, where the minimum length is MINIMUM_ABBREV. The
 	length may be exceeded to ensure unique object names.
+deltabase::
+	If the object is stored as a delta on-disk, this expands to the 40-hex
+	sha1 of the delta base object. Otherwise, expands to the null sha1
+	(40 zeroes). See `CAVEATS` section below.

I know existing description for other things nearby still talk about
SHA-1, but we can prepare ourselves better with something like:

	This expands to the object name of the delta base for the
	given object, if it is stored as a delta.  Otherwise it
	expands to the null object name (all zeroes).

+Note that the sizes of objects on disk are reported accurately, but care
+should be taken in drawing conclusions about which refs or objects are
+responsible for disk usage. The size of a packed non-delta object may be
+much larger than the size of objects which delta against it, but the
+choice of which object is the base and which is the delta is arbitrary
+and is subject to change during a repack.
+
+Note also that multiple copies of an object may be present in the object
+database; in this case, it is undefined which copy's size or delta base
+will be reported.

OK.

 SEE ALSO
 --------
 linkgit:git-show-ref[1]

--
https://github.com/git/git/pull/552